Abstract:
China is rich in deep coal resources. With the continuous depletion of shallow coal resources, deep coal mining is imperative. Currently, over 40 coal mines in China have reached or exceeded a mining depth of 1 000 meters, with the deepest reaching 1 510 meters, mainly distributed in the central and eastern regions and the northeastern mining areas. Additionally, some mining areas in the west, such as the Ordos, Longdong, and Binchang mining areas, have also entered deep mining. Compared with medium and shallow mines, deep mines are characterized by high ground stress, strong mining-induced disturbance, large deformation (in soft rock) and strong impact (in hard rock). The deformation of the surrounding rock in deep mine roadways is marked by strong dilatancy, strong rheology and severely impact damage . The stress environment and geomechanical properties of the surrounding rock in deep roadways were deeply analyzed, and the deformation and failure characteristics of the surrounding rock in deep soft rock roadways were studied. It was found that the large deformation in deep soft rock roadways was mainly caused by three types of deformation: dilatancy, rheology of coal and rock mass, and structural rheology. The mechanism of large deformation and instability of the surrounding rock in deep soft rock, high stress and strong mining-induced disturbance roadways was revealed. The concept of coordinated control of surrounding rock support, modification and pressure relief in deep roadways was proposed. The fundamental principle of this coordinated control was expounded. The spatio-temporal coordinated action of various surrounding rock control methods was analyzed. The principle of “three active” coordinated control of surrounding rock support, modification and pressure relief in deep roadways was clarified. Different coordinated control methods of surrounding rock in deep roadways were proposed. The “three-in-one” coordinated control technology of surrounding rock support, modification and pressure relief was developed, including high prestressed bolts and cables and thin spray active support, high-pressure splitting grouting active modification, and hydraulic fracturing active pressure relief technology. The grouting bolting with high pretension and pressure in synergy control technology was developed for the advanced section of the working face to strengthen support, forming a complete surrounding rock control technology for deep working face roadways (including gateway, open-off cut and advanced area). New materials for bolting, such as a 700 MPa ultra-high-strength, ultra-high elongation (30% post-fracture), and high-impact toughness bolt, was developed. Three types of high injectability, high adhesion and high strength grouting materials, including nano-modified coal and rock-friendly single-liquid inorganic-organic composite grouting materials and micro-nano double-liquid inorganic-organic composite grouting materials, and high strength and high toughness roadway surface spraying protective materials were developed. Other innovations include the development of high prestressed grouting bolts and cables with high pressure, as well as 35 MPa pneumatic and 45 MPa hydraulic high-pressure grouting pumps, plus a pressure-flow-density multi-parameter grouting monitoring system have been developed. Underground local hydraulic fracturing equipment and underground directional long horizontal borehole large-flow hydraulic fracturing equipment with high-pressure were developed. The complete set of coordinated control technology for deep roadway surrounding rock was systematically integrated and successfully applied in complex and difficult roadways in deep mining areas such as Xinji, Xinwen, Huaibei, Wanbei and Binchang, including deep soft rock roadways, ultra-deep high stress roadways, deep strong mining-induced disturbance roadways, deep soft and broken surrounding rock roadways and deep thick hard roof strong impact roadways. The deformation of the surrounding rock in roadways was significantly reduced, and the stability of the surrounding rock was significantly improved, which strongly support the safety and efficient production of deep coal mines. Finally, the development directions of the theory, technology, materials and equipment for the control of deep roadway surrounding rock in the future were prospected.